This invention relates to a forging device for forming a helical gear having crown-shaped teeth with the tooth thicker in the axial direction center of the twisted tooth than at both axial direction ends.
A prior art is disclosed in JP-B-6-98449. That is, a helical gear forging device in which a die having twist forming teeth is fitted for vertical sliding in the axially central part of a die holder through downward diminishing taper surfaces, a cylindrical material is placed on the die, and the device comprises a first and a second punches for pressing the material and the die from above, a counter punch in engagement with the lower end part of the die to restrict the downward movement of the material, and a rotary device for rotating the die holder in the direction opposite the direction in which the material is rotated with the die.
The above-described device of the prior art is the one in which the material is forced into the die, and twist teeth are formed on the outside circumferential surface of the material. Therefore, the thickness of the formed twist tooth is nearly constant over its entire length.